The present invention relates to a device for coating an optical fiber with a protective resin, and particularly relates to a device for evenly coating an optical fiber with resin which has a reduced number air bubbles and can be applied at a high drawing rate.
An optical fiber made of glass from the quartz group has been widely used as an optical fiber for communication transmission. Because the optical fiber is extremely weak when the fiber is flawed,the manufacturing process includes a step in which the fiber is covered with a protective resin just after the fiber is formed and before it can be damaged. An optical fiber is commonly coated with resin by a process as shown in FIG. 5. Optical fibers can be damaged by "micro-bending" or "macro-bending" depending on the severity of the external force. A damaged or bent optical fiber will result in increased transmission loss and a shorter useful life span.
As an example of the current optical fiber production processes, FIG. 5 shows a technique disclosed in U.S. Pat. No. 4,264,649 issued to Claypoole. Shown in FIG. 5 is a device used to apply a liquid resin onto the optical fiber, and the resin is later hardened by irradiation of ultraviolet rays or thermal heating. The optical fiber 1 is drawn through a nipple hole 11 and a nipple 2 and into a die 3. Contained in a gap between the corn like side surface 16 of the nipple 2 and the tapered side 13 of the die 3 is the resin 4 to be applied to the optical fiber 1. A meniscus 17 is formed as the optical fiber 1 is drawn through the pressure fed resin 4. The resin 4 is squeezed and shaped to the desired outer circumference as the optical fiber is drawn through the outlet hole 14. The entire apparatus is contained in a holder 5.
As the demand for optical fibers has grown, the optical fiber industry has enhanced its mass production techniques by increasing the drawing rate by which fibers are manufactured. However, with a device as shown in FIG. 5, at high drawing rates (i.e., over 500 m/min) air bubbles are mixed with the resin and the outer circumference of the optical fiber is not evenly coated with resin. Uneven resin coating can cause micro- or macro-bending in the fiber when an external force is applied or when the resin undergoes expansion or contraction as a result of temperature changes. Therefore, a device as shown in FIG. 5 has a limited drawing rate for acceptable fiber optic production.
Various innovations have been attempted in order to accomplish an evenly resin coated fiber at higher drawing rates. For example, as disclosed in Kar, U.S. Pat. No. 4,531,959, the resin is forced through a cylindrical body containing numerous holes positioned between a nipple and a die. The optical fiber is drawn through the center of the cylindrical body as it passes through the nipple and the die in an attempt to produce a bubble free and evenly resin coated optical fiber. Another innovation disclosed in Jochem, U.S. Pat. No. 4,644,898, purges the meniscus portion of the device with a low kinematic viscosity gas; furthermore, a central position of the resin coating device is mechanically adjustable. However, each of these techniques entails complicated devices which require fine adjustments for satisfactory optical fiber production. Therefore, they have proven to be difficult to easily use in mass production. The present invention solves both the air bubble and uneven coating problems while offering low maintenance equipment which can be operated at high drawing rates.